Method for manufacturing hollow engine valve

ABSTRACT

A method for manufacturing a hollow engine valve includes inserting a half-finished hollow shaft section in sequence into die holes which have different hole shapes, and sequentially drawing so as to reduce the outer diameter and the inner diameter of the hollow shaft section and stretch its length in stages. The half-finished product is subjected to heat treatment so that the hardness thereof is lower than or equal to a predetermined level. A shaft end sealing section is formed by increasing the wall thickness of the opening end of the hollow shaft section toward the inside of the opening and the gap in the shaft end sealing section is welded.

TECHNICAL FIELD

The present invention relates to a method for producing a hollow enginevalve which can simplify production steps and reduce production cost.

BACKGROUND ART

Among engine valves, various engine valves designed as follows arerecently provided along with the increase in output and performance ofan engine. An inside of the engine valve is formed to be hollow and thishollow portion is filled with metallic sodium serving as a coolant. Thisdesign reduces the weight, and improves the thermal conductivity by theaction of metallic sodium filled in the hollow portion, compared to asolid engine valve. A conventional method for producing such a hollowengine valve is disclosed in, for example, Patent Documents 1, 2.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent No. 4282900

Patent Document 2: Japanese Patent No. 4390291

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, in the conventional method for producing a hollow engine valve,the hollow engine valve as a finished product is obtained by producingmultiple members separately and then eventually joining the members toeach other. Accordingly, many steps must be performed to produce thehollow engine valve. Hence, this may make the production stepscomplicated and increase the production cost.

The present invention has been made to solve the problems describedabove, and an object thereof is to provide a method for producing ahollow engine valve which can simplify production steps and reduceproduction cost.

Means for Solving the Problems

In a method for producing a hollow engine valve according to a firstaspect of the invention for solving the aforementioned problems, inwhich a hollow stem portion of a semi-finished product is shaped into apredetermined shape by sequentially inserting the hollow stem portioninto a plurality of shaping holes different in hole shape tosequentially draw the hollow stem portion in such a way that an outerdiameter dimension and an inner diameter dimension of the hollow stemportion are reduced stepwise and a length of the hollow stem portion isincreased stepwise, the method for producing a hollow engine valve ischaracterized by comprising: subjecting the semi-finished product toheat treatment in such a way that a hardness of the semi-finishedproduct becomes equal to or less than a predetermined hardness; shapinga stem end sealing portion by causing a wall thickness of an openingedge portion of the hollow stem portion to be increased toward an innerside of the opening edge portion, by using a last one of the shapingholes which has a hole diameter adjusted; and joining gap portions ofthe stem end sealing portion together.

The method for producing a hollow engine valve according to a secondaspect of the invention for solving the aforementioned problems ischaracterized by further comprising adjusting a hole diameter of a stemshaping portion in the last one of the shaping holes, the stem shapingportion configured to shape the hollow stem portion.

The method for producing a hollow engine valve according to a thirdaspect of the invention for solving the aforementioned problems ischaracterized by further comprising injecting a coolant into the hollowstem portion before the drawing performed by using the last one of theshaping holes.

Effect of the Invention

In the method for producing a hollow engine valve of the presentinvention, the semi-finished product subjected to heat treatment in sucha way that the hardness thereof becomes equal to or less than thepredetermined hardness is shaped to have the wall thickness of theopening edge portion of the hollow stem portion increased inward, byusing the last shaping hole having the hole diameter thereof adjusted,and the gap portions of the stem end sealing portion shaped by thisincrease of wall thickness are joined together. By using this method,the number of parts forming the hollow engine valve 1 can be reduced.Thus, the method can simplify production steps and reduce productioncost.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] FIG. 1 is an overall configuration diagram of a cold forgingapparatus to which a method for producing a hollow engine valve of thepresent invention is applied.

[FIG. 2] Part (a) includes a vertical cross-sectional view of a die ofthe cold forging apparatus which is provided for an n-th drawing stepand a vertical cross-sectional view of a semi-finished product shapedwith the die, and Part (b) includes a vertical cross-sectional view of adie of the cold forging apparatus which has been conventionally providedfor the n-th drawing step and a vertical cross-sectional view of asemi-finished product shaped with the die.

[FIG. 3] FIG. 3 is a vertical cross-sectional view of a hollow enginevalve produced by the producing method of the present invention.

MODE FOR CARRYING OUT THE INVENTION

A method for producing a hollow engine valve of the present invention isdescribed below in detail by using the drawings.

Embodiment

First, as shown in FIG. 3, a hollow engine valve 1 produced by theproducing method of the present invention is used as an intake valve oran exhaust valve of an engine in a vehicle or the like. An inside of thehollow engine valve 1 is filled with metallic sodium N as a coolant.

The hollow engine valve 1 is one in which a valve umbrella portion 11, ahollow stem portion 12, and a stem end sealing portion 15 are shapedintegrally. A hollow hole 13 is formed in the inside of the hollowengine valve 1, extending through the valve umbrella portion 11 and thehollow stem portion 12. Moreover, although described in detail later, inthe stem end sealing portion 15, an opening edge portion on a base end(upper end) side of the hollow stem portion 12 is shaped to close bycausing the wall thickness thereof to be increased toward an inner sideof the opening edge portion, with the hollow hole 13 filled with themetallic sodium N. Lastly, gap portions in a center portion of the stemend sealing portion 15 are joined together.

Specifically, the hollow engine valve 1 is produced by using a coldforging apparatus 20 to be described later and the like. Metallic sodiumN is injected into the hollow hole 13 during the cold forging, and thejoining of the stem end sealing portion 15 is thereafter performed.Thus, the hollow engine valve 1 as a finished product can be obtained.Note that, the hollow engine valve 1 is sometimes not filled withmetallic sodium N depending on usage conditions.

Next, the configuration of the cold forging apparatus 20 is described byusing FIG. 1 and parts (a) and (b) of FIG. 2.

The cold forging apparatus 20 shown in FIG. 1 shapes the hollow enginevalve 1 by sequentially drawing (cold-forging) a semi-finished product 1a. A press bed 21 is provided in a lower portion of the cold forgingapparatus 20 while a ram 22 is provided in an upper portion of the coldforging apparatus 20 to face the press bed 21. The ram 22 is supportedto be moveable in a vertical direction.

Tubular dies Di1, Di2, Di(m−1), Dim, Di(n−1), and Din′ are provided on abottom face of the ram 22 in line along a conveyance direction of thesemi-finished products. Here, index m refers to m-th in the order andindex n refers to n-th (last) in the order. Moreover, m<n is satisfiedand m and n are each a positive integer equal to or larger than 3.

Shaping holes M1, M2, M(m−1), Mm, M(n−1), and Mn′ each having a circularhorizontal cross-section are opened respectively in center portions ofthe dies Di1, Di2, Di(m−1), Dim, Di(n−1), and Din′. The shaping holesare formed such that the inner diameters thereof are gradually reducedas the shaping holes are located more downstream in the conveyancedirection. Moreover, the lengths (depths) of the respective shapingholes M1, M2, M(m−1), Mm, M(n−1), and Mn′ are respectively L1, L2,L(m−1), Lm, L(n−1), and Ln, and the shaping holes are formed such thatthe lengths L1, L(m−1), Lm, L(n−1), and Ln are gradually increased asthe shaping holes are located more downstream in the conveyancedirection. In other words, these lengths are set such thatL1<L2<L(m−1)<Lm<L(n−1)<Ln is satisfied.

Meanwhile, semi-finished products 1 a, 1 b, 1 m, and 1 n, and the hollowengine valve 1 can be conveyed and positioned on the top face of thepress bed 21 by using conveyance means which is not illustrated.

The die Din′ is described by using parts (a) and (b) of FIG. 2.

The die Din′ is used to draw the semi-finished product 1 n shaped by thedie Di(n−1) and thereby obtain the hollow engine valve 1 as asemi-finished product (joining not yet performed). In the hollow enginevalve 1, the opening edge portion of the hollow stem portion 12 isclosed to bulge toward the inner side thereof, and the stem end sealingportion 15 is thereby formed. Specifically, in the cold forgingapparatus 20, the die Din′ is provided instead of a die Din usedconventionally to shape a hollow engine valve (valve body) 1 x whosehollow stem portion has a uniform wall thickness and whose opening edgeportion is opened.

As shown in part (a) of FIG. 2, the shaping hole Mn′ of the die Din′ isformed to have a length of Ln and includes a shaping portion (valveumbrella shaping portion) Man′ for eventually shaping an upper portionof the valve umbrella portion 11 of the hollow engine valve 1 and ashaping portion (stem shaping portion) Mbn′ for shaping the hollow stemportion 12 and the stem end sealing portion 15 of the hollow enginevalve 1, the shaping portion Mbn′ formed continuously with an upperportion of the shaping portion Man′. The shaping portion Man′ is formedto have an inner diameter of Dn at the largest portion while the shapingportion Mbn′ is formed to have an inner diameter of dn′.

The hollow engine valve 1 is shaped to have a length (height) of 1 n′ byperforming drawing with the die Din′ described above. Moreover, by thisdrawing, the hollow engine valve 1 is shaped in such a way that thehollow stem portion 12 and the stem end sealing portion 15 each have anouter diameter of dn′ and the hollow stem portion 12 has an innerdiameter of dn2.

Meanwhile, as shown in part (b) of the FIG. 2, a shaping hole Mn of thedie Din is shaped to have a length of Ln and includes a shaping portionMan for eventually shaping an upper portion of a valve umbrella portionof the hollow engine valve 1 x and a shaping portion Mbn for shaping ahollow stem portion of the hollow engine valve 1 x, the shaping portionMbn formed continuously with an upper portion of the shaping portionMan. The shaping portion Man is formed to have an inner diameter of Dnat the largest portion while the shaping portion Mbn is formed to havean inner diameter of dn which is larger than the inner diameter dn′(dn>dn′).

The hollow engine valve 1 x is shaped to have a length (height) of 1 n,which is larger than 1 n′ (1 n>1 n′), by performing drawing with the dieDin described above. Moreover, by this drawing, the hollow engine valve1 x is shaped such that the hollow stem portion has an outer diameter ofdn, which is larger than the outer diameter dn′, and an inner diameterof dn2.

In other words, compared to the die Din, the die Din′ is set in such away that the inner diameter dn′ is smaller than the inner diameter dn.By using this die Din′, the hollow engine valve 1 having the stem endsealing portion 15 for closing the opening portion of the hollow stemportion 12 can be shaped.

The hollow engine valve 1 is produced as follows. First, a solidround-bar-shaped material which is not illustrated is subjected to hotforging and the semi-finished product 1 a is thereby shaped. Thereafter,the semi-finished product 1 a is subjected to heat treatment in such away that the hardness thereof becomes equal to or less than apredetermined hardness. Next, the semi-finished product 1 a having thehardness equal to or lower than the predetermined hardness is positionedat a point on the press bed 21 of the cold forging apparatus 20 whichcorresponds to the die Di1.

Then, elevation and decent operations of the ram 22 and conveyanceoperations and positioning operations of the conveyance means areperformed sequentially and n times of drawing are sequentially performedwith the dies Di1, Di2, Di(m−1), Dim, Di(n−1), and Din′. As a result,the semi-finished product 1 a is sequentially shaped into thesemi-finished products 1 b, 1 c, 1 m, and 1 n. This shaping causes theouter diameter dimension and the inner diameter dimension of each hollowstem portion to be reduced stepwise and the length of each hollow stemportion to be increased stepwise, and the hollow engine valve 1 iseventually formed.

Subjecting the semi-finished product la to heat treatment in such a waythat the hardness thereof becomes equal to or less than thepredetermined hardness has the following effect. In each of thesemi-finished product 1 a and the semi-finished products 1 b, 1 c, 1 m,and 1 n thereafter, it becomes easier to increase the wall thickness ofthe hollow stem portion and harder to increase the length of the hollowstem portion as the hardness of the semi-finished product becomessmaller.

By drawing the tempered semi-finished product 1 n with the shaping holeMn′ of the die Din′ adjusted to have the inner diameter of dn′ asdescribed above, the hollow engine valve 1 can be shaped to have thewall thickness of the opening edge portion of the hollow stem portion 12increased toward the inner side thereof. Moreover, in the drawing withdies Di1, Di2, Di(m−1), Dim, and Di(n−1), since hole shapes of therespective shaping holes M1, M2, M(m−1), Mm, and M(n−1) of these diesare not adjusted from the conventional ones, the shaping is performedwith the opening edge portion of each hollow stem portion opened.

Incidentally, in the drawing with the die Din′, when the opening edgeportion of the hollow stem portion 12 is not closed toward an inner sidethereof by performing the drawing once, the drawing is performedmultiple times until the wall thickness of the opening edge portionincreases and the opening edge portion is thereby closed. Moreover,since the shaping holes M1, M2, M(m−1), Mm, M(n−1), and Mn′ do not presslower portions of the valve umbrella portions in the semi-finishedproducts 1 a, 1 b, 1 m, and 1 n, the outer diameters of the umbrellaportions of the semi-finished products at the largest portions aremaintained at D_(o).

Here, the hollow hole 13 is already filled with metallic sodium N afterany one of the steps of drawing with the dies Di1, Di2, Di(m−1), Dim,and Di(n−1) in the cold forging apparatus 20. Hence, after the drawingto close the opening edge portion is performed, the hollow engine valve1 as a finished product can be produced by joining the gap portions ofthe stem end sealing portion 15 together by, for example, filler weldingor non-filler welding. Incidentally, the stem end sealing portion 15 isnot exposed to an exhaust gas of a high temperature. Hence, the joiningof the gap portions may be performed by blazing or the like, instead ofwelding.

In the method of producing a hollow engine valve of the presentinvention, the semi-finished product 1 n subjected to heat treatment insuch a way that the hardness thereof becomes equal to or less than apredetermined hardness is shaped to have the wall thickness of theopening edge portion of the hollow stem portion 12 increased toward aninner side thereof, by using the shaping hole Mn′ of the die Din′adjusted to have the inner diameter of dn′. Thereafter, the gap portionsof the stem end sealing portion 15 shaped by the increase in wallthickness are joined together. By using this method, the number of partsforming the hollow engine valve 1 can be reduced. Thus, the method cansimplify production steps and reduce production cost.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a hollow engine valve producingapparatus which is designed to produce hollow engine valves different inshape in a single producing apparatus by making dies replaceable.

1. A method for producing a hollow engine valve in which a hollow stemportion of a semi-finished product is shaped into a predetermined shapeby sequentially inserting the hollow stem portion into a plurality ofshaping holes different in hole shape to sequentially draw the hollowstem portion in such a way that an outer diameter dimension and an innerdiameter dimension of the hollow stem portion are reduced stepwise and alength of the hollow stem portion is increased stepwise, the method forproducing a hollow engine valve characterized by comprising: subjectingthe semi-finished product to heat treatment in such a way that ahardness of the semi-finished product becomes equal to or less than apredetermined hardness; shaping a stem end sealing portion by causing awall thickness of an opening edge portion of the hollow stem portion tobe increased toward an inner side of the opening edge portion, by usinga last one of the shaping holes which has a hole diameter adjusted; andjoining gap portions of the stem end sealing portion together.
 2. Themethod for producing a hollow engine valve according to claim 1,characterized by further comprising adjusting a hole diameter of a stemshaping portion in the last one of the shaping holes, the stem shapingportion configured to shape the hollow stem portion.
 3. The method forproducing a hollow engine valve according to claim 1, characterized byfurther comprising injecting a coolant into the hollow stem portionbefore the drawing performed by using the last one of the shaping holes.